Fuel cell stacks are electrochemical devices that produce water and an electric potential from a fuel, which is typically a proton-liberating source, and an oxidant. Many conventional fuel cell stacks utilize hydrogen gas as the proton source and oxygen, air, or oxygen-enriched air as the oxidant. Fuel cell stacks typically include many fuels cells that are fluidly and electrically coupled together, often between common end plates. The fuel cell stack receives flows of hydrogen gas and air from suitable sources and distributes these flows to the individual fuel cells in the stack. The fuel cell stack includes manifolds and other delivery conduits to deliver and remove fluids to and from the fuel cells within the fuel cell stack. Conventionally, a fuel cell stack includes current collectors that are adapted to be electrically connected to an external load applied by an energy consuming device so that the electrical output produced by the fuel cell stack may be used to satisfy the applied external load.
The fuel cells in the fuel cell stack include anode and cathode regions that are separated by an electrolytic barrier, which may take the form of an electrolytic membrane. Hydrogen gas is delivered to the anode region, and oxygen gas is delivered to the cathode region. Protons from the hydrogen gas are drawn through the electrolytic membrane to the anode region, where water is formed. While protons may pass through the membranes, electrons cannot. Instead, the electrons that are liberated by the protons passing through the membranes travel through an external circuit to form an electric current.
Fuel cell systems may operate efficiently over a given range of electrical outputs. If the electrical output is greater than an upper threshold value, the fuel cell stack may generate excessive heat and/or dehydrate the electrolytic membranes contained therein, which may lead to irreparable damage to the fuel cell stack. In contrast, if the electrical output is less than a lower threshold, the fuel cell stack may not generate enough heat for efficient operation and/or otherwise may be operating inefficiently due to this reduced output. Energy consuming devices may apply an electrical load over a wide range of values depending on the energy demands of the energy consuming device, including electrical loads that are outside the efficient operating range of the fuel cell system. Thus, there exists a need for systems and methods to extend the electrical output range over which the fuel cell system may efficiently provide electrical power.